Conventionally, as an image reading apparatus mounted to an image forming apparatus such as a copier, a facsimile machine, or a multifunction peripheral, a contact image sensor (CIS) using a unity magnification optical system, with which the size of an image reading apparatus can be reduced, has become widely used instead of a CCD used for an reduction optical system.
Also, the use of a color contact image sensor in order to read color original images has been increasing.
FIG. 6A is a schematic configuration diagram of a reading unit of an image reading apparatus that includes a conventional color contact image sensor, and FIG. 6B is a schematic configuration diagram showing an enlarged view of a portion of the color contact image sensor.
The image reading apparatus is configured by an original reading unit 200 and an automatic original feeder 300, and the original reading unit 200 includes a color contact image sensor unit (hereinafter also referred to as a “CIS unit”) 110 that reads an image on one face of a transported original.
The CIS unit 110 includes three line image sensors 111, 112 and 113 for the colors R, G and B, in which photoelectric transducers for reading mutually different colors are arrayed in a sub-scanning direction X1 of an original to be read, and photoelectric transducers for reading the same color are arrayed in a main scanning direction (direction perpendicular to the page). The CIS unit 110 irradiates the read face of the original with light from a light source unit 145, the light reflected on the read face forms an image on the line image sensors 111, 112 and 113 for the colors R, G and B with an SLA (Selfoc lens array; “Selfoc lens” is a registered trademark) 146, for example, and thereby image information is read. Note that Patent Document 1 discloses a color contact image sensor unit in which line image sensors for the colors R, G and B are disposed in this order at a two-line pitch. The color contact image sensor unit of Patent Document 1 includes line sensors for the colors R (red), G (green) and B (blue) arrayed with different colors in a sub-scanning direction and the same colors in the main scanning direction of an original to be read, an RB data bus switching unit that performs a first switching process in which, with respect to image data read by the line sensors for the colors R, G and B, data of any two colors are switched and data of the remaining one color is allowed to pass without switching, an inter-line correction unit that outputs image data for the three colors R, G and B obtained by the RB data bus switching unit performing the first switching process as a RGB data set, and an RB data bus switching unit that receives image data obtained by the inter-line correction unit performing the inter-line correction process, and switches again the image data pieces of the two colors that have undergone the first switching process, and outputs the resultant data.